How I brought down drug-taking Lance Armstrong, by David Walsh

David Walsh delivering the annual Cudlipp lecture at the LCC. Photograph: Ana Escobar

"I am not an investigative journalist... I wish I was an investigative journalist... I don't have the talent to be a sports reporter..."

David Walsh, the multi award-winning journalist, was not indulging in false modesty. He was simply being honest, the character trait that has shone through all he has achieved in his career.

His confession about his supposed journalistic weaknesses was made last night while giving the Hugh Cudlipp annual lecture. It was unlike any lecture that has gone before and it riveted the audience at the London College of Communication (LCC).

Walsh, the Sunday Times's chief sportswriter, told the story of his dogged pursuit of the cheating champion cyclist Lance Armstrong with clarity and wit. Example of the latter: "I am a bit of a lawyer's nightmare because I have a conviction but no evidence."

That conviction - call it a hunch or an intuition - occurred in 1999 and was based on Walsh's inside knowledge of professional cycling. A young French rider, Christophe Bassons, had written a column for the newspaper Le Parisien in which he suggested that Tour de France riders were taking drugs.

Walsh, who had already had doubts about Armstrong's astonishing post-cancer performances, noted how Armstrong treated Bassons. He pulled him up during one of the Tour stages and told him he had no right to be a professional cyclist and what he was writing was bad for cycling.

"If Armstrong was anti-doping, Christophe Bassons would have been his friend not his enemy," said Walsh. "Why bully him?" It confirmed his suspicion that Armstrong, who went on to win that 1999 Tour, was a drug-taker.

It was the beginning of a 13-year journalistic odyssey. In 2001, he confirmed a connection between Armstrong and an Italian doctor, Michele Ferrari, who was under investigation for supplying performance-enhancing drugs to cyclists. Walsh discovered that Armstrong's name was in hotel registers in the town where Ferrari lived.

He wrote about it. Nothing happened to Armstrong, but in the following years whistle-blowers came forward to provide him with more evidence, notably Armstrong's masseuse, Emma O'Reilly.

Her accusations were the centrepiece of Walsh's book, L.A. Confidential, written along with French sports journalist Pierre Ballester in 2004. Armstrong, who went on denying taking drugs, dismissed the accusations and then sued the Sunday Times over a related article, leading to the paper paying out £1m in a libel settlement.

But Walsh, who found few friends and supporters among the rest of the journalistic cycling fraternity, would not let go. He obtained more evidence from one of Armstrong's former teammates, Frankie Andreu, and his wife Betsy. He knew Armstrong was lying.

It wasn't until June 2012 that Walsh was finally vindicated when the United States Anti-Doping Agency (USADA) banned Armstrong from competitive cycling for life for doping offences and said he had been engaged in "the most sophisticated, professionalised and successful doping program that sport has ever seen."

In January 2013, Armstrong appeared on the Oprah Winfrey show and admitted that he had taken drugs during every one of his seven Tour de France victories.

Walsh, who told the LCC audience several times that he refused to fall into the trap of so many sports journalists - being "a fan with a typewriter" - drew lessons from his experience:

"A good story is always worth pursuing"... "if you're right, good people will come out to help you"... "it's ok to swim against the tide"... and Britain's libel laws "are seriously deficient - they have zero interest in the truth".

He said that he never worried about being unpopular with his peers. "A good story is always worth pursuing," he said, "no matter how difficult pursuing it might be."

After Walsh's speech, the Daily Mirror editor, Lloyd Embley, called him "an example and inspiration to us all."

The Hugh Cudlipp lecture, founded in 2005 to commemorate the former Mirror group editorial director, was sponsored by the Daily Mirror.

At the conclusion, Jim Norton was named as the winner of the Hugh Cudlipp award for student journalism 2014 for an article in the Scottish edition of the Daily Mail.